“No one can call me a sourpuss,” she declared. “I have a big foot in the joy camp.”

She is the author of “Dancing in the Streets,” a history of “collective joy,” she notes, and a lot of fun at parties. So her new book, “Bright-sided: How the Relentless Promotion of Positive Thinking Has Undermined America,” should not be mistaken for a curmudgeonly rant. It is serious social history.

Many of the 17 books that Ms. Ehrenreich has written during the past three and half decades have taken her into alien worlds. In her fantastically successful 2001 book, “Nickel and Dimed,” for example, she details her experience of trying to get by on the salary of an unskilled, minimum-wage worker. By contrast, this newest volume is based on her stay in a world that she became intimately familiar with: the smiley-faced, pink-ribboned, positive-thinking culture that surrounds breast cancer patients.

Ms. Ehrenreich found out she had the disease in 2000, and the news left her dazed, fearful and, most of all, angry. What she found when she sought information and support, however, was cheerfulness, and that shocked her.

“There were exhortations to be positive,” Ms. Ehrenreich said. She had stopped for lunch recently in Manhattan’s theater district after meeting with her publisher at Metropolitan Books, and before returning to Alexandria, Va., where she moved two years ago to be close to her daughter and grandchildren. Smartly dressed in pants and a sweater with black rectangular glasses that frame her blue eyes, Ms. Ehrenreich, 68, looks like someone who is content to be fashionable rather than fashion forward.

The unrelenting message was “that you had to be cheerful and accepting and that you would not recover unless you were,” said Ms. Ehrenreich, who also writes frequently for The New York Times. Most infuriating, she added, was the advice to “consider your cancer a gift.”

Every rosy affirmation — the advertisements for breast cancer teddy bears and other tchotchkes, the inspirational slogans (“When life hands out lemons, squeeze out a smile”), and the politically correct language (“victim” and “patient” are avoided because they suggest passivity) — sharpened her keen sense of outrage.

“I have to say I took it personally,” she said. At one point she wrote a rant on Komen.org, a Web site that focuses on breast cancer education and research, about her anger over environmental carcinogens, endless battles with insurance agencies, toxic treatments and “sappy pink ribbons.” She recalled a typical response to her post: “You need to run, not walk, to get therapy. You can’t get better without poisoning your system.”

Her eyes widened at the memory. “If I don’t get better, it’s my fault,” she continued. “It’s a clever blame-the-victim sort of thing.”

Ms. Ehrenreich underwent a mastectomy and chemotherapy and wore a wig to cover her hair loss during her book tour for “Nickel and Dimed.”

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Over the next few years, however, she kept encountering the same smiling insistence elsewhere that a positive outlook itself was the solution to problems. It had infiltrated the large career-counseling industry that serves the unemployed; the Ivy League, where “positive psychology” has nested in the curriculum; the best-seller list, where “The Secret” has taken up residence; mega-churches run by evangelists; and conferences for motivational speakers.

Then the financial crisis hit. “Wham,” she said. “It was so clear to me that it was connected.” The relentlessly optimistic forecasts about subprime mortgages and endless increases in real estate values were the product of the positive-thinking culture. One of the fundamental tenets of the literature, Ms. Ehrenreich said, is to surround yourself with other positive thinkers and “get rid of negative people.”

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Meanwhile, a background in science — she has a Ph.D. in biology — made Ms. Ehrenreich especially skeptical of pseudoscientific claims that positive thinkers often cite.

In “Bright-sided,” she traces the roots of the nation’s blithe sunniness to a reaction against Calvinist gloom and the limits of medical science in the first half of the 19th century. Starting with Phineas Parkhurst Quimby, perhaps one of the first American New Age faith healers, she draws a line to Mary Baker Eddy, the founder of Christian Science; the psychologist William James; Ralph Waldo Emerson; Norman Vincent Peale, who published “The Power of Positive Thinking” in 1952; and the toothy television minister Joel Osteen, who preaches the gospel of prosperity.

To Ms. Ehrenreich, the reliance on one’s personal disposition shifts attention from the larger social, political and economic forces behind poverty, unemployment and poor health care. “It can’t all be fixed by assertiveness training,” she said wryly.

Ms. Ehrenreich found that the more she listened, the surlier she became. All that shiny optimism, she said, was “like sitting in a warm bubble bath for too long.” Luckily she found other churlish comrades, scholars and doctors who were similarly skeptical of undimmed positivity.

“We began to call ourselves the Negatives,” said Micki McGee, a sociologist at Fordham University and the author of “Self-Help, Inc.: Makeover Culture in American Life.” The group would meet on occasion and discuss their research and the news of the day. The thread of positive thinking that runs through self-help culture says, “If you dream it and believe it, it becomes reality,” Professor McGee explained. “That kind of thinking contributes to the economic bubble that we just saw explode in enormous ways. Barbara’s take on it is very important.”

Richard Sloan, a professor of behavioral psychology at Columbia, is a more recent member of the Negatives. He has written at length about the absence of scientific evidence showing links between prayer and healing in his book “Blind Faith: The Unholy Alliance Between Religion and Medicine.”

“There is some relatively recent evidence of the benefits of positive affect, but not the simplistic approach that is advocated by coaches that all you need to do is be happy,” he said. “There is no evidence that trying to put on a happy face makes a difference.” Rather, those who are characteristically more optimistic may have an advantage over those who aren’t, but, he said, “you just can’t change who you are very easily.”

The Negatives are quick to note that they are positive about some things. Despair is not the only alternative to positive thinking, Ms. Ehrenreich maintains; a spiral of negativism can be just as bad as a positive one. She is, as Mr. Osteen would say, living her “best life.”

Still, if people insist on seeing her as a “messenger of doom,” she gracefully accepts the role: “I will see what I can do to awaken us to this mass delusion.”

A version of this article appears in print on October 10, 2009, on Page C3 of the New York edition with the headline: Author’s Personal Forecast: Not Always Sunny, but Pleasantly Skeptical. Order Reprints|Today's Paper|Subscribe